Electrical contactor for movable shafts



' June 2l, 1949.l R. w. GEORGE 2,473,705

ELECTRICAL CONTACTOR FOR MOVABLE SHAFTS Filed April 24, 194s listened June 2,1, 1949 Ralph w. George, Riverhead, N. Y., assigner to Radio Corporation of America, a. corporation of Delaware Application April 24, 1945, Serial N0. 590,011`

This invention relates to improvements in grounding means for movable shafts used in electrical apparatus.

In radio apparatus it is known to use shaft grounding arrangements for grounding the condenser tuning shaft. Among the difficulties experienced with these known shaft grounding contactors are that they provide (1) undesirably large inductance paths from the shaft to the grounded panel or partition, (2) low contact pressure between shaft and support, and (3) unreliable electrical contact between shaft and support when the radio apparatus is subjected to rough vtreatment and all 'sorts of weather conditions.

The present invention overcomes the foregoing dimculties and provides a highly novel and improved contacting means for a metallic movable shaft used in electrical apparatus, which possesses the following advantageous characteristics: (1) It furnishes a low inductance connec- 'tion and hence a lowv impedance path between the shaft and the supporting partition or panel, (2) it provides high contact pressure between the shaft and support which is uniformly distributed around the shaft, (3) itis rugged and capable of use '1n Army and Navy equipment subjected to the rigors of service (for example, dust, Weather, rough treatment), and (4) it has long life with minimum resistance to movement of the shaft for the corresponding high contact pressure employed.

A more detailed description of the invention follows in conjunction with a drawing, wherein: y

Fig. 1 illustrates a perspective view of the complete shaft supporting unit before mounting in electrical apparatus;

Fig. 2 illustrates an exploded view of the elements of the unit of Fig. 1 before they are assembled, and f Fig. 3 illustrates the manner in which the unit of Fig. 1 ts into a metallic partition or panel for electrically grounding a rotatable condenser shaft in radio apparatus.

Throughout the figures the same parts are represented by the same reference numerals.

Referring to Figs. 1 and 2 in more detail, the shaft grounding unit comprises a. metallic spring contact washer I, a metallic bushing 2 having at one end a threaded metallic tube 3, and a clamp nut 4 having a threaded hole in its center for use with the threaded tube 3.

The exploded view of Fig. 2 illustrates the man- 5 Claims. (Cl. 173-324) of radially runningslots 5 and is formed to the desired shape before assembly. This spring washer fits into a recess or shoulder S on one end of bushing 2 and is soft soldered thereto. After the washer is thus secured to the bushing it is staked or swaged to the bushing at a plurality of ner in which the. elements are assembled during the process of manufacture. The spring washer I is a thin round metallic disc having a plurality l vfor the desired contact pressure.

points 6 to assure additional mechanical strength and a strong bond between washer andbushing.

The spring washer l is shaped so that, a plurality In several embodiments of the invention suc.

cessfully tried out in practice, the bushing 2 was made out of brass, the spring washer i was made out of beryllium copper, and the entire assemblage plated with chromium to provide a long wearing surface with a minimum of binding uetween the shaft and points of contact. Rhodium plating instead of chromium plating is also to be recommended.

The'manner in which the invention is used to electrically ground a metallic condenser tuning shaft lll through a low inductance connection to the panel is shown in Fig. 3. The metallic shaft is labeled 8, preferably silver or rhodium plated when used in very high frequency systems, and

electrically joins together the rotor plates ora condenser C whose stator plates are joined to one terminal of an inductance coil L. The other terminal of inductance coil L is connected to one wall of a groundedshielding container 9 or partition. Condenser C and inductance L form a tuned circuit which is representative of any tuning system desired in a radio frequency system.

The shaft 8 is grounded at oppositely disposedl metallic partition walls W of the shielding container 9 by means of two grounding units of the invention. To each of these partition walls W is mounted the large end of bushing 2 with the clamping nut 4 to assure good electrical contact therebetween` VThe tapered contact ingers l provide high con- I tact pressure between the shaft 8 (uniformly around its periphery) and the bushing 2. The shaft l0 is rotatable within the bushing by means of a tuning knob II with a minimum of resistance Cne end E of the shaft Ill is shown provided with a thrust ball bearing. by way of example 3 only, while some intermediate point T is provided with another ball bearing support.

The shaft supporting unit of the invention permits either or both a rotatable or a sliding motion of the shaft, while always grounding the shaft electrically to the panel through a low inductanceI path. It is of rugged character and can withstand rough'treatrnent. Moreover, it is highly reliable, from an electrical standpoint, and may be used in electrical apparatus operating anywhere in a frequency range extending from very low frequencies up to very high frequencies of the order f thousands of megacycles.

Although the invention has been shown with a bushing having a threaded tubular member at one end for cooperation with a nut to secure the assemblage to a partition or panel, it should be understood that the invention is not limited to such a feature since, if desired, the threaded portions may be eliminated and the bushing secured to the partition in any suitable manner such as by screws or riveting.

What is claimed is:

1. An electrical contactor for a movable metallic shaft, comprising a metallic bushing having a central aperture larger than the diameter ol the shaft to be accommodated thereby, said bushing having a recess at one end thereof bounded by a circular `wall of larger internal diameter than the diameter of said aperture, a disc-like metallic washer securely fastened at its periphery to said circular wall of said bushing and having a plurality of uniformly spaced contact lingers forming an aperture which is smaller than but registers with the aperture of said bushing, said contact fingers forming tapered segments which are joined together at their wide bases, said contact fingers being bent to provide a substantially cylindrical surface slotted at the edges of said segments and which cylindrical surface is adapted to make positive mechanical and electrical contact on its interior with the shaft which it surrounds.

2. Means for electrically connecting a movable metallic shaft in electrical apparatus to a metallic panel through a low inductance path, comprising a metallic bushing having an aperture through which said shaft extends, said bushing having a recess at one end thereof bounded by a circular wall of larger internal diameter than the diameter of said aperture, a disc-like metallic washer secured at its periphery to said circular Wall of said bushing and having a plurality of contact fingers forming an aperture registering with the aperture of said bushing, said contact fingers having interior surfaces adapted to make positive electrical and mechanical contact with said shaft, both said'bushing and washer having highly electrically conducting surfaces, a threaded tubular member at the other end of said bushing for passing through a hole in said panel, and a clamping nut for operative association with said tubular member to thereby fasten said bushing to said panel.

3. Means for electrically connecting a movable metallic shaft in electrical apparatus to a metallic panel through a low inductance path, comprising a metallic bushing having an aperture through which said shaft extends, said bushing having a recess at one end thereof bounded by a circular wall of larger internal diameter than the diameter of said aperture, a disc-like metallic washer secured at its periphery to said circular wall of said bushing and having a plurality of tapering contact fingers forming an aperture registering with the aperture of said bushing, said contact fingers having small fiat interior surfaces adapted to make positive mechanical and electrical contact with said shaft, both said bushing and washer having highly electrically conducting surfaces, and means for securing said bushing firmly to said panel.

4. An electrical contacter for a movable metallic shaft, comprising a metallic bushing having a central aperture larger than the diameter of the shaft to be accommodated thereby. a disclike metallic washer securely fastened to said bushing at one end and having a plurality of unlformly spaced contact fingers forming an aperture which is smaller than but registers with the aperture of said bushing, said contact fingers forming tapered segments which are joined together at their wide bases, said contact fingers being bent in the same direction to provide a substantially cylindrical surface slotted at the edges of said segments and which cylindrical surface is adapted to make positive mechanical and electrical contact on its interior with the shaft, said bushing having a threaded tubular element at its other end, and a clamping nut for said threaded tubular element.

5. An electrical contacter for a movable metallic shaft, comprising a metallic bushing having a central aperture larger than the diameter of the shaft to be accommodated thereby. said bushing having a recess at one end thereof bounded by a circular wall of larger internal diameter than the diameter of said aperture, a disc-like metallic washer securely fastened at its periphery to said circular wall of said bushing and having a, plurality of uniformly spaced contact 1ingers forming an aperture which is smaller than but registers with the aperture of said bushing, said bushing having a threaded tubular element at its other end, a clamping nut for said threaded tubular element, said contact ngers forming tapered segments which are joined together at their wide bases, said contact fingers being bent in the same direction toward said tubular member to provide a substantially cylindrical surface slotted at the edges of said segments and which cylindrical surface is adapted to make positive m'echanical and electrical contact on its interior with the shaft which it surrounds.

RALPH W. GEORGE.

REFERENCES CITED The following refererrces are of record in the file of this patent:

UNITED STATES PATENTS 

